Multi-Cavity Insulating Glass Units: Design and Energy Efficiency Trends

1. Multi-Cavity Insulating Glass Units

2. GANA is a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members available on request. • This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

3. Learning Objectives • Identify the drivers that lead to the selection of multi-cavity glazing. • Understand the design and construction of multi-cavity glazing. • Understand the challenges of multi-cavity glazing constructions. • Select the correct multi-cavity construction to meet certain performance characteristics.

4. Outline • Introduction • Drivers to selection • Design, challenges and benefits • Multi-cavity IG options and considerations

5. Introduction • Multiple cavity insulating glass units (Multi-cavity IGs) refer to an IG with more than one air space in the unit • Effective method to improve energy efficiency of the glazing • Improved U-factors are needed to meet the demands of stricter energy codes • Multi-cavity IGs are already widely used in Europe and their adoption is increasing in North America and Canada • This presentation will describe the use and features associated with Multi-cavity IGs.

6. Energy Efficiency Trends

7. Drivers of energy efficiency • Building Codes • ASHRAE and IECC; IgCC • Standards • ASTM International and NFRC • Certification • LEED and Passive House Institute; Living Building Challenge; Green Globes • Government • US DOE; EPA Energy Star • Economics • Rising energy costs increase the importance of energy efficiency

8. Changes in Recent Years • Energy codes increased stringency by 30-38% • ASHRAE 90.1-2010 and 2013 • 2012 and 2015 International Energy Conservation Code (IECC) • Increased code adoption and enforcement • Even where code enforcement is lax, these changes will still be seen in the specifications. • New “high performance green building codes” • ASHRAE 189.1-2011 and 2014 • 2012 and 2015 International Green Construction Code (IgCC)

9. Increased Stringency of ASHRAE 90.1 • Decrease in regulated loads energy use since 90.1-2004: • 30% • 38%

10. What will these changes mean? • Increased stringency means more complex window design • Low-e basically required everywhere • Thermally broken frames required in most of the country • Increase in use of argon and warm edge spacers • Certain regions need thermally broken frame with two low-e coatings • #2 traditional low-e, #4 interior low-e • Multi-cavity glazing is an alternative method to achieve the improved energy efficient designs above

11. What will these changes mean? • Multi-cavity glazing is needed in certain zones • ASHRAE 90.1-2016: Triple glazing for Zone 8 • 2012 and 2015 IECC: Triple glazing for Zones 7 & 8 (mostly Alaska and Canada) • Green codes are set at 5-10% lower U-factor than ASHRAE 90.1 and IECC, so they will also encourage multi-cavity glazing in Zones 6-8 (zone 8 being northernmost Alaska and Canada).

12. Multi-Cavity IG Design

13. Multi-cavity IG Design Outboard lite • Double-Glazed IGU • Insulating glass units of two lites of glass typically separated by a spacer and sealant system with one desiccated (dehydrated) cavity • Multiple-Cavity IGU • Units of three or more lites / layers with two or more desiccated cavities with outer glass lites and with intermediate layers of glass, film or other materials Inboard lite Spacer & sealant system Outboard lite Center lite Inboard lite Spacer & sealant system

14. Multi-cavity IG Design • Glazing lites are held apart by spacer “system” that includes spacer, desiccant and sealants • Spacer system serves four principle functions: • Maintain cavity spacing (spacer) • Removing moisture from cavity (desiccant) • Prevent moisture from penetrating space (spacer & sealants) • Retain argon or other gas fill within space (spacer & sealants)

15. Spacer options for Multi-cavity IGs • Multi-cavity IGs can have a number of spacer designs • Center glass lite(s) using spacer(s) for each cavity • Center glass lite(s) using a single grooved spacer(s) for both cavities • Center suspended film(s) using spacer(s) for each cavity Graphics courtesy of the Insulating Glass Manufacturers Alliance

16. Design • Multi-cavity IGUs may incorporate different glass or other materials: • Annealed glass (low strength) • Heat-strengthend glass (medium strength) • Tempered glass (high strength) • Laminated glass (strength, blast or acoustic) • Suspended film • Polycarbonate • Coated/tinted

17. Design • Coated Glass Incorporation • Coatings may be present on any one or more surfaces of glass, depending upon the desired performance characteristics. • Coatings may include high performance sputtered or pyrolytic variants. • Glass coatings are readily available for energy savings, aesthetics, solar control, IR and/or UV reflection, bird strike deterrence or easy cleaning features. • Film Incorporation • One or more plastic film(s) may be used as a center barrier. • Plastic film(s) may be coated for low-e performance characteristics. • In general these IGUs are lighter in weight.

18. Design • Low-e Coatings • The main benefits of Low-e coatings are: • U-factor improvement • Solar control • The location of one or more low-e coating(s) within the IGU affects thermal and solar performance: • A Low-e coating located close to the exterior surface of an IG generally results in lower SHGC values. • Positioning Low-e coating(s) closer to the interior generally result in higher SHGC values. • Multiple coatings, often in combination with tinted glass, provide aesthetically pleasing and enhanced thermal performance results. • Generally, only one Low-e coating is used per air space.

19. Design • Spacer types include: • Rigid: metal, plastic or combination that are extruded, roll formed or assembled to create rigid spacer. Are typically filled with desiccant. • Flexible: thermoset or thermoplastic rubbers and plastics with rigid internal components to maintain glazing space. Typically have desiccant integral to spacer.

20. Design • Multi-cavity IGUs should be designed and specified based upon environmental stresses. • External loads should be considered. • Edge design and sealant depths all need to be evaluated. • Cavities within the IGU may be pressure balanced or unbalanced. • Balanced cavity pressure may be achieved in many ways, but generally a small equalization hole is drilled in the corner of interior plies. • Consideration should be made for heat-treating the center lite due to potential thermal stress issues. • More information may be obtained from IGMA’s Design Considerations for Multi-Cavity IGU, document TM-1300(www.igmaonline.org).

21. Performance • Multiple performance attributes to be considered: • Durability (internal condensation/fogging; gas retention) • Double transmission paths • Higher internal pressurization due to temp • Fabrication complexity • Thermal Factor (U-Factor, SHGC, condensation resistance) • Dual low-e • Krypton for narrower profile • Unbalanced for Kr/Ar • Typical double vs. triple IG performance – various configurations • Visible transmission (VT) reduction • Surface 1 condensation • Acoustical • Mass effect • Airspace effect

22. Performance: Durability • Tested to ASTM E2190 specification series for: • Resistance to internal moisture condensation • Resistance to internal volatile fog formation • Ability to retain insulating gas • Multi-cavity IGU complexities • Multiple edge-seal transmission paths in typical constructions • Higher internal pressurization of exterior cavity due to reduced heat energy transfer to interior • Fabrication complexity due to multiple spacer/sealant construction

23. Performance: Thermal • U-factor • Multiple low-e coatings significantly improve COG U-factors; below 0.20 Btu/hr-ft2-OF • Typically coatings are in separate glazing cavities to optimize thermal performance and minimize heat build-up potential within a single cavity • Krypton provides optimal performance in narrower glazing gapcompared to air or argon, but could increase cost • Multiple coatings reduce visible light transmission (VLT) through the multiple cavity IGU as compared to a double glazed with similar glass components

24. Performance: Thermal • U-factor - Typical Double-Glazed IGU performance (Courtesy of WESTLab)

25. Performance: Thermal • U-factor - Typical Triple-Glazed IGU performance (Courtesy of WESTLab)

26. Performance: Thermal • U-factor - “High-Performance” Triple-Glazed IGU performance (Courtesy of WESTLab)

27. Performance: Thermal • Solar Heat Gain Coefficient (SHGC) • Multiple low-e coatings can significantly reduce the solar heat gain coefficient (SHGC) as compared to a double glazed with similar glass components. • Condensation Resistance • Significantly lower U-factor yields higher interior glass surface temperatures and, subsequently, greater resistance to interior condensation • As low unit U-factor substantially reduces heat transfer from interior to exterior, surface #1 temperatures may be very close to exterior air temperature. Further radiant cooling may lead to exterior moisture condensation or even frost formation under specific environmental conditions.

28. Performance: Acoustical • Mass Law effect • Approximate 6 dB improvement in sound transmission loss (STL) for every doubling of system mass • Example – adding identical third lite of glass to a double IGU to create a triple IGU should add 50% more mass = 3 dB STL improvement • Airspace effect • Approximate 3 dB improvement in STL for every doubling of glazing space gap • May offset gains of adding additional glass lites if glazing space not maintained • Example – adding third lite to a double IGU without increasing the respective glazing space gaps may reduce the effectiveness of each gap • Decoupling effect with suspended films • suspended films may provided additional STL improvements by disruption of sound through the use of dissimilar materials • STL improvements do not directly correlate to improvements in OITC or STC ratings of the overall system

29. Performance: Acoustical • Data are for the glazing only and is not applicable for the glazing installed in a window system • 3 ft x 7 ft units (915 mm x 2130 mm); performance will vary for other sizes • Frame design, air leakage, spacer system, glazing system and other variables may reduce ratings 5 or more points from those published in these tables from AAMA TIR-A1-04 -Sound Control for Fenestration Products . Courtesy of AAMA TIR-A1-04 www.aamanet.org

30. Multi-Cavity Considerations

31. Challenges • Thermal Stress • Load Resistance/Rating • Weight • Coating Detection • Gap Optimization • Optical Effects • Condensation • Fabrication considerations

32. Challenges • Multi-cavity IGs give many additional design considerations compared to double glazing: • Thermal Stress • Absorbed solar heat in the middle lite(s) of a multi-cavity IG cannot easily escape • Multiple Low-e coatings and/or insulating gas on both sides can result in thermal stress breakage of annealed inner lites • Using a Low-E coating or tinted glass on the center lite(s) typically requires heat treating • Contact the primary glass manufacturer for assistance

33. Challenges • Load Resistance / Rating • Greater glass stress, deflection and edge seal pressure due to magnification of temperature changes and air pressure differentials • Load Resistance Rating – ASTM E1300 • procedure GTF x LSF = 2.4/4.9/9.7 (AN/HS/FT) • Weight: Multi-cavity IGs use additional glass and other materials which increase weight • Added glass and materials can result in more than a 50% weight increase, over a double glazed IG • It is important to design the sash or frame properly to compensate for this additional weight; consider use of a thinner center lite of glass

34. Challenges • Exterior Condensation • Low-e coated products are available for surface #1, which can minimize the effects of exterior condensation • Hydrophilic products may lessen the appearance of condensation • Gap Optimization • Reference LBNL’s WINDOW simulation software program • Optical Effects • Propensity for greater reflection, distortion, and deflection • Compared to a double glazed unit, a multi-cavity IG will have increased reflectivity and decreased light transmission

35. Challenges • Condensation • Improved thermal performance may lead to reduction in surface #1 glass temperature • Under certain conditions this temperature may drop below the dew point, causing condensation • Exterior condensation is not a design flaw, but a consequence of the lower U-factor • Exterior condensation is most prevalent on clear nights, and when the window has a clear line of sight to the night sky

36. Challenges • Fabrication considerations • Fabrication equipment may limit available product configuration • Gas fill in all cavities • Coating multiple surfaces • Maximum dimensions L x W and thickness • Use of laminated product • Installation • Glazing system needs to support unit thickness and weight • On-site handling may be different than conventional single cavity • Consult Fabricator/Glazing contractor • Compatibility • As with traditional single-cavity units, project specification documents should require the compatibility of all glazing sealants and other components • Failure to use compatible sealants may result in premature failure of insulating glass units • Refer to GANA Glazing Manual for more information

37. Learning Objectives • Identify the drivers that lead to the selection of multi-cavity glazing. • Understand the design and construction of multi-cavity glazing. • Understand the challenges of multi-cavity glazing constructions. • Select the correct multi-cavity construction to meet certain performance characteristics.

38. This concludes the American Institute of Architects Continuing Education System Program.

39. Glass Association of North America (GANA) Insulating Division 800 SW Jackson St Ste 1500 Topeka, KS 66612 Phone: (785) 271-0208 Fax: (785) 271-0166 www.glasswebsite.com